1. Field of Invention
The invention relates to the technical field of an impeller for a liquid pump provided in the fuel tank of vehicle and pumping a liquid.
2. Description of Related Art
This type of liquid pump is, for example, a fuel pump arranged in a fuel tank. In general, a fuel pump having the following structure is well known. More specifically, an impeller is rotatably mounted in a pump chamber, which is formed with an intake port and an outlet port at its outer-radial portion, and fuel flowing from the intake port is pumped from the outlet port based on a rotation of the impeller. The impeller of the fuel pump has a structure as shown in FIGS. 8(A)-8(C), for example. That is, a disk plate member (impeller) 14 having a predetermined plate thickness is formed with a plurality of vanes 14a, which extend substantially radially or approximately perpendicular to a tangent to the circumferential direction, and a plurality of vane grooves 14b are interposed between adjacent vanes 14a, at the outer periphery. The vanes 14a and vane grooves 14b are formed on both plate surfaces (both sides) so that they can be alternately positioned on opposite sides of the intermediate portion M of the disk plate member 14. In the impeller, the vane groove 14b has an inclined surface 14c, which is formed so that the inner-radial edge portion reaches the plate surface of the disk plate member 14. With the rotation of the impeller 14, fuel flowing from the intake port flows from the inner-radial side of the inclined surface 14c to the outer-diameter side thereof along the inclined surface 14c. Then, the fuel is rotated while forming a vortex flow between the inclined surface and a ring recess groove for a passage formed in the impeller casing that constitutes a pump chamber, and is pumped from the outlet port formed at the outer-radial side (see the outlined arrow shown in FIG. 8(A)). In the impeller, the fuel flow is analyzed based on CFD (Computational Fluid Dynamics); as a result, the following problems (see FIGS. 8(B) and 8(C)) are found. First, there exists a flow colliding with a rotating direction (see arrow FIG. 8(A)) trailing surface 14d which generates, an impact loss. Second, another vortex flow, different from the previously described vortex flow, is formed backward from a rotating direction leading surface 14e such that cavitation results. Third, stagnation is generated in the thickness direction intermediate portion of the outer-radial portion of the impeller 14 which generates a counter flow. The problems are a factor in reducing the pump""s efficiency. The mentioned phenomena are believed to occur from the following cause. That is, the vortex flow flows later than a rotational speed of the vane 14a; on the contrary, the shape of the vane 14a (vane surface) of the impeller 14 is parallel to the thickness direction (rotary shaft direction) surface. Further, the outer-diameter edge portion of the vane 14a and the inner-radial surface of the impeller casing closely face each other.
In order to solve the problem, the impeller disclosed in Japanese Patent Application Publication (laid-open) No. 9-511812 has been proposed. As shown in FIG. 9(A), vanes 15a of an impeller 15 are formed between a plurality of through holes 15b formed along a circumferential direction of a disk plate member. A radially inner surface 15c of the through hole 15b is formed into a surface inclined with respect to the intermediate portion M (inner-diameter edge portion reaches plate surface) so that each plate surface is further inwardly inclined, and the inclined surface is used as a fuel passage. On the other hand, the plurality of vanes 15a are formed with a ring portion 15d at the outer radial side. Further, in the impeller 15, each vane 15a is formed in a state of being inclined to the rotary shaft of the disk plate member, that is, to the intermediate portion M of the disk plate member so that both plate surface sides of the disk plate member are positioned to a rotating direction leading side. The shape of the vortex flow is similar to that of the vane 15a (through hole 15b) so as to reduce a collision (impact loss) of the flow against a rotating direction trailing surface 15e of the through hole 15b. 
In the impeller 15, the fuel flow is analyzed based on the CFD in the same manner as the conventional example; as a result, as shown in FIGS. 9(B) and 9(C), the following points are found. First, a counter flow by stagnation is reduced in the outer-diameter portion of the impeller 15. Second, the collision of fuel with the vane 15a, that is, the collision with rotating direction leading and trailing surfaces 15f, 15e of the through hole 15b is reduced. Third, a main vortex flow is smoothly formed in a state of running along the radial inner surface 15c of the through hole 15b. Therefore, the pump""s efficiency is considered as improved. However, as seen from FIG. 9(B), in the fuel flow, a small vortex flow, which is different from the main vortex flow guided to the radially inner surface 15c and flowing to the outer-radial side, is formed backward of the rotating direction leading surface 15f of the vane groove 15b. Further, there exist flows which collide with the rotating direction leading and trailing surfaces 15f, 15e. As a result, like the conventional example, the cavitation and impact loss is generated as ever; therefore, these are factors in reducing the pump""s efficiency.
On the other hand, in recent years, it is greatly desired to achieve a high output of a fuel pump, and to simultaneously make the fuel pump compact. In order to achieve the purpose, there is a need to further improve the pump""s efficiency, and this is a problem to be solved by the invention.
The invention has been made in view of the circumstances, and therefore, an object of the invention is to solve the problems found in the prior art.
In order to achieve the object, the invention provides an impeller for liquid pump, the impeller provided in a pump chamber formed with an intake port and an outlet port, which is rotated so that a liquid taken from the intake port can be pumped from the outlet port, comprising:
a plurality of through holes penetrating the thickness of a disk plate member and formed at an outer periphery of the disk plate member along the circumferential direction thereof; and
a plurality of vanes formed between adjacent through holes,
a radial inner surface of each though hole being inclined from a thickness direction intermediate portion to an inner-radial side in order to guide a liquid to the thickness direction intermediate portion side,
the radial inner surface being inclined so that its rotating direction leading side is positioned to the inner-radial side in order to secure an area for guiding the liquid wider.
By doing so, the inflow portion of liquid, that is, the radial inner surface of the through hole has a wider area, and the flow rate of the main vortex flow increases. Therefore, pump efficiency can be improved.
Further, the invention provides the impeller for a liquid pump, wherein a radial outer surface of each though hole is inclined so that its rotating direction leading side is positioned to the inner-radial side.
Further, the invention provides the impeller for a liquid pump, wherein the radial outer surface of each though hole is inclined from the thickness direction intermediate portion to an outer-radial side of the through hole.
Further, the invention provides the impeller for a liquid pump, wherein the pump chamber is formed with a ring recess groove for a fluid passage, which faces a vane forming portion, and an inner-radial edge portion of the ring recess groove faces the rotating direction leading surface of the through hole; on the other hand, an outer-radial edge portion of the ring recess groove faces the rotating direction trailing surface thereof.
Further, the invention provides the impeller for a liquid pump, wherein the rotating direction leading and trailing surfaces of the through hole are inclined from the thickness direction intermediate portion to the rotating direction leading sides.
Further, the invention provides the impeller for a liquid pump, wherein the rotating direction leading and trailing surfaces of the through hole are inclined with respect to a radial line of the impeller so that their outer-radial sides are positioned to the rotating direction leading sides.